Process for controlling chrysosporium lignorum in lignocellulosic material

ABSTRACT

A process is provided for the selective control of Chrysosporium lignorum in wood chip piles that are stored in the open for long periods of time, by means of a nickel compound, without deleterious effect on the microbiological activity of other nonharmful organisms.

United States Patent Inventors Anders Assarsson Sundusen; Thomas Nilsson, Skarholmen, both of Sweden Appl. No. 743,964 Filed July 11, 1968 Patented Nov. 2, 1971 Assignee Mo och Domsjo Aktiebolag Ornskoldsvik, Sweden Priority July 18, 1967 Sweden 10,067/1967 PROCESS FOR CONTROLLING CHRYSOSPORIUM LIGNORUM IN LIGNOCELLULOSIC MATERIAL 18 Claims, No Drawings U.S. Cl 162/72, 162/1, 195/10,]95/121, 195/123 lnt.C| D2lc 3/20 [50] Field of Search 195/8, 10, 55,56,731, 110, 122, 121, 123; i62/96,71, 160, 161, 72

[56] References Cited UNITED STATES PATENTS 3,493,464 2/1970 Bowers et a1. 162/161 3,486,969 12/1969 Nilsson et a1. 162/72 Primary Examiner-A. Louis Monacell Assistant Examiner-Gary M. N ath Attorney-Janes & Chapman ABSTRACT: A process is provided for the selective control of Chrysosporium lignorum in wood chip piles that are stored in the open for long periods of time, by means of a nickel compound, without deleterious effect on the microbiological activity ofother nonharmful organisms.

PROCESS FOR CONTROLLING CHRYSOSPORIUM LIGNORUM IN LIGNOCELLULOSIC MATERIAL This invention relates to the control in wood particle piles of the deleterious action of rotand slime-producing micro organisms on lignocellulosic materials, and particularly the control of the mold fungus Chrysosporium lignorum, using a nickel compound.

The prevention of attack of lignocellulosic materials such as timber and wood by micro organisms is a particularly serious problem in the wood-handling industries, such as the pulp and timber industry. Wood-processing plants have insatiable appetites for wood, and therefore it is necessary to keep large supplies of raw wood in the form of logs, chips, and timber on hand, to keep the plant operating at times when wood may be in short supply, or hard to cut and ship. Since indoor storage is costly, the supplies are kept outdoors, and can be stored for long periods of time before they can be processed. The processed wood may also have to be stored for long periods, due to variable market demand, and shipping conditions. During such storage, the wood is subject to attack from micro organisms. The longer the wood has to be stored, the more serious the deterioration of the wood, due to microbiological actlon.

Fiberboardand pulp-processing plants also have to store their raw material, naked or bark-covered wood chips, outdoors in huge piles for long periods of time. In the processing of wood chips by the sulfite pulping process, it is, however, desirable to store the chips in the open for several months or longer, because this subjects the resins in the chips to decomposition by biological action. The chips thus have a much lower resin content, and pitch problems in the mill and resin problems in the pulp are avoided.

However, it is not unusual for the piles of chips to be attacked at the same time by wood rot organisms, and this attack can be so severe that they are no longer fit for use in the manufacture of pulp and fiberboard. Bark-containing chips are most subject to rot attack when stacked in tightly packed areas as in chip piles, where temperatures in the interior of the pile can reach relatively high levels, of almost 100 C., because of heat liberated in the course of chemical oxidation reactions accompanying microbiological attack by thermophilic fungi. As a result, the storage of wood chips presents a special problem from the aspect of deterioration of the wood, since wood decomposition is most prevalent in wood chip piles in which the highest temperatures are generated, and which contain a relatively high percentage of moisture, and

since lignocellulose material in the form of chips of a high surface area presents a considerable greater surface area for attack than wood in the form of logs or timber. Because of this, harmful micro organisms can cause considerable damage in a relatively short time. Besides that, at certain higher chip pile temperatures, the rate of activity of the micro organisms may be increased.

The deterioration of the wood due to attack by harmful micro organisms has not heretofore been susceptible to being counteracted by destroying the harmful micro organisms. The reason is that some types of microbiological attack actually aid in preparing the wood for processing. Microbiological attack is of two general types (a) attack on the lignocellulosic molecule, which in effect decomposes the wood, and (b) attack on the wood extractives, which are discarded anyway in the wood processing. Rot fungi are in the first category. Certain micro organisms, for instance, certain mold fungi, lack the ability to reduce the polymeric carbohydrates of the lignocellulosic molecule, and instead attack the extractive materials and low molecular carbohydrates of the lignocellulosic material as their nutrient source. They also complete by antibiosis with the harmful rot fungi, and in this way actually assist in preventing deterioration of the cellulose.

When the wood is treated with a microbiocidal substance, both types of micro organisms are usually destroyed; so that one loses the helpful microbiological action as well, and this is undesirable.

To achieve a proper balance of harmful and helpful balance of microbiological activity therefore, the storage of wood and particularly wood chips usually envisions a period of time that permits the desiredattack by micro organisms to a certain extent, but without exceeding the storage period desirable for this deterioration, so as to avoid the loss of wood due to deterioration because of the attack of the harmful micro organisms. This requires a nice adjustment of storage temperatures and storage times, since a difference of merely a few days in storage time may give rise to difficult problems.

The most damaging fungus in chipv piles is Chrysosporium lignorum. This fungus was isolated only recently, by Thomas Nilsson and reported for the first time in Svensk Papperstidning 68 No. I5, 495 (1965) under the proposed name Chrysosparium lignorum, which name was not, however, finally adopted. This is a particularly rapid-growing fungus, and its rotting activity is consequently very high. Chip piles provide particularly favorable development conditions for this fungus, because of the temperature and the moist conditions. The other most harmful micro organisms are primarily different types of known rot fungi, such as Stereum hirsutum and Poria ambiqua. Blue-stain-producing micro organisms, such as Scytalidium Iignicolumn, Scytalidium album, etc. do not destroy wood to the same extent as the harmful micro organisms, but they do discolor the wood, which influences the brightness of the unbleached sulfite pulp.

Mold fungi which are not in the category of harmful fungi because their attack can be useful in preparing the wood chips for processing include Gliocladium viride, Spororrirhum rhumophile, Penicillium cylindrosporum, Aspergillusfumigalus, Al- Iescheria terresm's, Trichoderma lignorum, Gliocladium deliquescens, Gliocladium roseum, Penicillium funiculosum, Penicillium rubrum, Penicillium roqueforri, Humicola slellara, Humicola insolens, Humicola Ianquinosa, Talaromyces duponri, Thermoascus auranliacus, Mucar pusillus, Mucor miehi, Malbranchella pulchella, Myriocaccum albomyces, Torula thermophila, Chaelomium thermophile, Stilbella tlrermophile, and others.

ln accordance with this invention, it has been determined that it is possible to control the growth of the mold fungus Chrysosporium lignorum completely, without appreciably diminishing the desirable attack by the helpful mold fungi, and this can be done by treating the wood with a nickel compound that supplies nickel in available or soluble form. These compounds not only give complete control of Chrysosporium lignorum, but they also control at least to a significant extent, and in many cases completely, the rot fungi, such as Stereum hirsutum and Poria ambiqua. In this way, the attack of micro organisms which decompose the cellulose and hemicelluloses of the lignocellulosic material is inhibited, whereas the desirable attack of other micro organisms on the extractive substances, i.e., the resins, etc., of the lignocellulose, is not materially diminished. This makes it possible to store wood chips and other particulate forms of wood in such a manner that the desirable microbiological attack can be fully controlled and regulated and the undesirable attack minimized or eliminated simply by control of the amount of nickel compound that is present with the wood.

The nickel that is known to be effective is nickelic nickel, i.e., Ni. Nickelous compounds may also be effective, especially if under the conditions of storage nickelous nickel can be oxidized to nickelic nickel.

It is important that the nickel compound supply nickel in an available form, in which it can react and affect the micro organisms. For this purpose, it is best that the nickel compound be soluble in the liquids that are present on or in the wood. Such liquids are aqueous, for the most part, and consequently the nickel compound is preferably water soluble. However, these fluids can in some cases be acidic or alkaline, depending upon the nature of the wood and other conditions. and therefore the nickel compound is preferably one that is soluble in such media, if they are present.

Also suitable are nickel compounds which are soluble in polar solvents of an organic or inorganic type, such as a]- cohols, ketones, esters, halogenated hydrocarbons and aromatic hydrocarbons. However, aqueous solutions of nickel compounds are less costly, and are, preferred for treatment of the lignocellulosic material.

Within these limitations, any nickel compound can be used as a source of'available nickel, whether inorganic or organic. By soluble," it is meant that the nickel compound is soluble in the fluid, such as water, in an amount of at least 0.0001 g./cc. and preferably, at least 0.01 g./cc. The nickel compound should be io'nizable, and furnish a sufficient concentration of nickel ion to the liquorto be toxic to Chrysosporium lignorum and any other organisms to be controlled. However, it has been found that the concentration of the nickel need not be high; the micro organisms are apparently inhibited by very small amounts of nickel in solution; a concentration of as little as 0.0001 g./cc. is effective to some extent. Thus, nickel compounds in which the nickel is solubilized by virtue of fonnation of a slightly ionized nickel complex with some other substances can be used, even if the nickel is ionized only rather insignificantly in such complexes. Nickel ammonia and nickel cyanide complexes are'exemplary. Such complexes can be formed with other fungicidal metals, such as copper, tin and manganese, if desired, so as to impart to the fungicidal compositions the activity of such elements as well.

Thus, as the nickel compound, there can be used finely divided metallic nickel (which can be solubilized and dissolved in an acidic or alkaline liquor, as the hydroxide or some salt form or soluble complex), inorganic nickel compounds, such as nickel chloride, nickel nitrate, nickel sulfate, nickel carbonate, nickel cyanide, nickel ammonium sulfate, nickel nitrite, nickel bromide, nickel fluoride, nickel iodide, nickel bicarbonate, nickel hydroxide, nickel oxide, nickel ferrocyanide, diacrotetramine nickel nitrate, Ni(Nl*i;,),,(l-i O) (N nickel sulfite, nickel bromate, nickel bromide hexamine NiBr 6NH nickel perchlorate, nickel hexamine chloride NiCl 6NH nickel acid fluoride, nickel fluosilicate, and nickel hypophosphite, as well as organic nickel compounds, such as nickel fonnate, nickel acetate, nickel dimethyl glyoxime, tetrapyridine nickel fluosilicate, nickel stearate, nickel oleate, nickel oxalate, nickel phenolate, nickel cresolate, and nickel pentachlorophenolate.

The nickel compound can be applied to the wood particles by any desired technique. A solution of the nickel compound in water or an organic solvent can be employed. Such a solution can be sprayed, brushed, painted or coated on the wood particles or the wood particles can be dipped or immersed or floated in such a solution. It is also possible to dust a finely divided or particulate solid nickel compound on the surface of the wood, allowing it to soak in by the action of moisture present on the surface of and in the wood, by rain, and other moisture provided during storage in the open. For wood chip piles, the most convenient method of application is by adding a solution of the nickel compound to the wood chips while they are in the transport line before distribution on the pile.

The amount of nickel compound that is applied will depend upon the desired degree of control of the activity of the micro organisms. For optimum control of the harmful Chrysosporium lignorum and rot fungi, and minimum interference with the desirable action of the helpful micro organisms, the amount of nickel calculated as Ni provided by the compound should be within the range from about to about 5,000 milligrams per kilogram of lignocellulosic material. Preferably, the amount of nickel compound provides an amount of nickel within the range from about to about [00 milligrams per kilogram.

The process of the invention is applicable to any kind of lignocellulosic material in particulate form, including both natural or bark-containing and debarked; sticks, kindling, wood chips, sawdust, wood flour, splinters, and other types of wood particles, cellulose pulp, prepared either by the sulfate or sulfite process, or any other form of chemical processing,

cellulose fluff, and cellulose flour. Lignocellulosic material derived from any kind of wood can be treated, including lignocellulosic material from pine, spruce, fir, birch, beech, cedar, aspen, cypress, oak, maple, eucalyptus, gum, sycamore, cherry, mahogany, teak, and locust.

The following examples in the opinion of the inventors represent preferred embodiments of their invention.

EXAMPLE 1 Colonies of harmful wood-decomposing micro organisms were cultivated using four different forms of wood as nutrient carbon sources, and the toxicity thereto of different nickel compounds was determined, using the following test procedure. The wood sample was mixed with water containing sterilized agar-agar, after which the mixture was transferred to glass containers 10 cm. in diameter to form plates 5 mm. thick. in this way, agar-agar plates were prepared containing (l) finely ground pinewood; (2) powdered pinewood (holocellulose) from which the lignin had been removed by oxidation with sodium chlorite; (3) chlorite-oxidized powdered pinewood, which had been extracted with 5 percent potassium hydroxide solution, then neutralized with acetic acid, and precipitated with ethanol, separated and washed (hemicellulose); (4) Bjiirkman-lignin, a pure lignin produced according to special standardized methods. Svensk Papperstidning, 59 No. 13, pp.477-485 (1956). The amount of wood as a carbon source in each agar-agar plate was l25 mg. Control plates of each type were reserved, and nickel compound then applied to the other plates in the form of an aqueous solution containing nutrient salts in such a quantity that the concentration of nickel in each case was 45 parts per million. The nutrient salt composition was as follows:

Parts by Weight KHZPO, 350 K,HPO, r50 NH,N03 500 M so,-7H,o MnSO,-4H,O 50 FeSO, l5 znso, 2 Thiamine 100 H,o 1,000

The degree of inhibition of the micro organisms in the test plates was evaluated as a percentage of the growth after the same period of time of the untreated micro organisms in the control plates, to which the same nutrient salt solution was added but with no nickel compound. The radii of the respective growths was compared, as the measure of growth. The growth was in all cases less in the agar-agar plates treated with nickel-containing solutions. The results obtained with the various test organisms are set out in table I.

l Powdered pine from which the lignin had been removed by oxidation with sodium chlorite.

Z Chlorite-oxidized powdered pine wood extracted with 5% KOH, neutralized, precipitated with ethanol, separated and washed.

3 Pure lignin produced according to special standardized methods.

NorE.-N=Deleterious. ND =Nondeleteri0us.

It is evident from the results set out above that Chrysosporium lignorum was 100 percent inhibited, in all cases. On the other hand, Gliocladium viride, a nondeleterious mold fungus, was not inhibited fully, and could continue its helpful activity. it is apparent from this that by this procedure by adjustment of 5 the amount of nickel compound, and the storage time, it is possible to obtain any desired degradation of the lignin resins and other extractive substances without deleterious decomposition of the lignocellulose.

The blue-stain-producing fungi was also inhibited to a certain extent. These, however, are not as harmful as Chrysasporium Iignorum.

EXAMPLE 2 Example 1 was repeated, using exactly the same test procedure, with finely ground pine wood in agar-agar. Several nickel compounds were employed, as noted in table ii. The degree of inhibition of the various test organisms is set out in the table:

EXAMPLE 3 Tests were carried out to determine the amount of loss of wood materials in spruce chips and birch chips inoculated with different wood-decomposing organisms, when controlled using various amounts of nickel sulfate, compared with certain known fungicides. The loss in weight of the wood chips was used as the measure of the amount of deterioration or decomposition of the wood. The application of the test fungicide was by way of immersion of the chips in solutions thereof at different concentrations. The surplus solution was allowed to drain off, and the chips were then stored. The organisms inoculated were Chrysosporium lignorum, Srereum hirsutum and Poria ambiqua. The results are given in table Ill.

It is evident that the nickel sulfate is virtually as effective as mercuri ehloride, in obtaining complete inhibition of each of these deleterious micro organisms, when a sufiicient amount is applied to the wood. However, mercuric chloride is poisonous, and its use is restricted for safety reasons, whereas TABLE II Inhibiting effect in percent Nickel Nickel Nickel dimethyl Nickel Nickel Mold fungi Blue stain-producing fungi sulphate oieate glyoxime chloride nitrate Chrysosporium lignorum, D 100 100 100 100 100 Gliocladium viride, ND 60 80 65 60 65 Scytaldr lrcum, D 25 25 25 Scutaldiu'm a m, D 85 85 90 90 85 eacem, ND 95 95 95 95 05 Dnctulomyces thermophilua, 90 90 90 90 90 Rhizopus arrhizus, ND... 100 100 100 100 100 Sporotn'chum ihermophile, 70 70 60 Paecylu'myces variotz', N D 90 95 90 90 95 Aspergillus fumigatus, ND 75 80 Allescllcria terrestris, ND 70 80 70 70 70 Penicillium cylindrosporum, ND 5 20 20 15 20 NOTE.D =Deleterious. ND Nondeleterlous.

The data further show that the type of nickel compound has very little effect on the degree of inhibition. Evidently, any source of nickel that provides nickel in an available or soluble form is effective in the purpose of the invention.

The most significant point in these results is that Chrysosparium lignorum was completely controlled. This is the most harmful of the micro organisms in wood chip piles, and it means that the uniform quality of the wood chips during 5 long periods of storage can now be maintained, by application of the process of the invention.

the nickel compound is not poisonous and therefore can be used freely. Neither the copper sulfate nor the sodium pentachlorophenolate in the very large concentrations used was able to give complete control of these micro organisms.

EXAMPLE 4 Newly chopped fresh spruce chips was treated by spraying with 200 parts per million of nickel sulfate and sodium pentachlorophenolate. One untreated portion was reserved as a control. All of the chips were then stored in plastic bags in an oven for 3 months to simulate the conditions existing in chip storage stacks. The oven temperature was held at 40 C. throughout the test period.

The chips were then subjected to microbiological examination. The control chips which had no fungicide showed good growths of Chryrosporium lignorum and traces of rot fungi. The chips to which nickel sulfate had been added showed no Chrysosporium lignorum, or other rot fungi. There were colonies of molds observed, however. The chips treated with sodi- TABLE III Weight losses in percent Sodium Fungicide Control pentaconceutration (N o fungichloro- Nicke Microorganism (mg/liter) eide) CuSO4 HgClz phenolate sulphat 25 50 Chryaouporium lipnorum on spruce chips, D 7.0 .3

7. 1, 000 3. 2 2, 500 2. 5 100 5. 9 Stemnn himuum on birch chips, D 500 9. 9 5. 5 1, 000 4. 8 100 6. 9 Pon'a amblqua on birch chips, D 500 8. 8 4.7 1,000 1.0

Norm-D =Deleterlous um pentachlorophenolate contained Erne 7 Chrysosporium lignorum; it was nofftiii'y'ihhibiteij in the case ofthe nickelsulfate-treated chips.

The weight of wood lost and the amount of extract (resin) in the wood extracted with dichloromethane according to the TAPPI Standard Test Method were then determined, and compared with the control to which no fungicide had been added. The results are shown in table IV.

It is evident from the table that the losses in wood weight when treated with nickel sulfate were only half those of the untreated wood, and that the treatment according to the invention gave a better resin decomposition, since the extract content was reduced. On the other hand, sodium pentachlorophenolate prevented the decomposition of the resin altogether, since the extract content was virtually unchanged, and resulted in the loss of more wood than when the nickel sulfate was used.

EXAMPLE The effects of nickel treatment when storing chips in large commercial-size piles was determined by spraying the chips with nickel sulfate (NiSO '6H- O) in a proportion of 200 parts per million of the dry wood, as the pile was built. A second pile was built up, using the same wood chips but untreated. A third pile of the same wood chips was sprayed with nickel sulfate and a suspension of Gliocladium viride spores. These piles were all of the same shape and size, and were stored outdoors for 3 months.

The temperature generated in the control pile composed of untreated wood chips-behaved normally, rose rapidly to 45 C., and remained substantially stable throughout the test period of 3 months. In the two piles treated with nickel sulfate, the temperature rose rapidly to 35 C., and was constant for 2 weeks. The temperature then fell, but remained above that of the surroundings for the remaining test period.

The piles were taken down after 3 months storage, and the 'nicroflora investigated. It was found that the wood in the control pile which contained no nickel sulfate had been attacked by rot and blue-staining fungi. In certain localized portions, Chrysasporium Iignorum was also well established, and had caused the wood to decompose to a great extent. No rot and no blue-staining fungi were found, but the majority of these fungi were Gliocladium viride. In the pile treated with both nickel salt and the addition of Gliacladium viride spores, the Gliocladium spores content was higher than in the nickeltre ated pile, but the microflora were essentially the same for the two piles treated with nickel sulfate, with and without the Gliocladium spores. This shows that the nickel was effective in controlling the growth of the flora in both these piles.

Analyses were made of the chip samples placed in the three piles at the beginning of the storage period. In order to assess 70 i the amount of wood losses, volume weight measurements were made, and special sacks were weighed. These sacks were weighed at the beginning and at the end of the storage period. The values shown in table V are the average values, taken from samples of each type.

TABLE V Raw volume Weight loss Weight Before storage Chips 400 After 3 months storage Control ships 374 4.6 Chips, Ni-treated 391 2.l Chips, Ni Gliocladium 388 2.5

treated According to the analyses, the loss of wood substances for the untreated wood chips lay between 4.5 and 6.5 percent, whereas the loss of wood in the case of chips treated with nickel was 2.2 to 4.5 percent. Thus, the weight losses in the case of the wood treated with nickel sulfate were reduced by more than 50 percent. When producing unbleached or bleached sulfite pulp from the nickel-treated wood chips, number 15-20, no disadvantages were observed. Nickel in the waste liquor tested up to 40 ppm. did not affect the fermentability of the liquor to alcohol, nor did it have any deleterious effect in the purification of waste water by the activated sludge process.

Example 6 A pile of bark-containing pine and spruce chips was built during the summer in a fiberboard-manufacturing plant. The chips were treated in blowlines with nickel sulfate at a concentration of 200 ppm. by weight of the dry wood. The temperature in the pile rose rapidly to from 55 to 60 C.. and remained at this level until autumn, when the temperature of the pile began to fall. During the winter, the temperature within the pile became stable at between 20 to 30 C. whereas in previous winters when untreated chips were stored under like conditions the temperature rose to between 65 to C. On the other hand, the freezing of the treated chips was no greater in the case of the untreated chips.

Sample sacks containing weighed chip samples showed a loss in wood after 8 months storage of 3 percent. The corresponding loss of wood for untreated chips having the same bark content was from 10 to 15 percent.

It is evident from the results that Chyrsosparium Iignorum and other rot fungi were well inhibited. The increase in the pile in the course of the test period showed that the activity of the nondeleterious fungi was slowed, but was not sufficiently inhibited to prevent the obtainment of the benefits of such activity. It is apparent that by adjustment of the proportion of nickel sulfate, any desired activity of the nondeleterious fungi can be obtained.

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:

1. A process for the control of the growth in wood particles of the mold fungus Chrysosporium lignorum, without appreciably diminishing the desirable attack by nondeleterious mold fungi, which comprises treating the wood particles with a nickel compound that supplies nickel in available or soluble form, and storing the treated wood particles under conditions favoring the desirable attack by nondeleterious mold fungi, whereby such attack proceeds while growth of Chrysosporium lignorum is substantially inhibited by the nickel compound.

2. A process in accordance with claim 1, in which the control at least to a significant extent of rot fungi such as Stereum hirsutum and Poria ambiqua is also obtained. 7

3. A process in accordance with claim 1, in which the wood in the form of wood chips.

4. A process in accordance with claim 1, in which the wood is cellulose pulp.

5. A process in accordance with claim 1, in which the nickel compound provides Ni nickel.

6. A process in accordance with claim 1, in which the nickel compound is an inorganic nickel salt.

7. A process in accordance with claim 1, in which the nickel compound is an organic nickel salt.

8. A process in accordance with claim 1, in which the nickel compound is applied in the form ofa solution in a liquid.

12. Wood particles in accordance with claim 11 in which resistance to rot fungi is also provided.

13. Wood particles in accordance with claim 11 in the form of wood chips.

14. Wood particles in accordance with claim 11 in the form of cellulose pulp.

15. Wood particles in accordance with claim 11, in which the nickel compound is present in an amount to provide from about 5 to about 5,000 mg. nickel per kg. ofwood.

16. Wood particles in accordance with claim 11 in which. the nickel compound provides Ni nickel.

17. Wood particles in accordance with claim 11 in which the nickel compound is an inorganic nickel salt.

18. Wood particles in accordance with claim 11 in which the nickel compound is an organic nickel salt.

* i i YIK 

2. A process in accordance with claim 1, in which the control at least to a significant extent of rot fungi such as Stereum hirsutum and Poria ambiqua is also obtained.
 3. A process in accordance with claim 1, in which the wood is in the form of wood chips.
 4. A process in accordance with claim 1, in which the wood is cellulose pulp.
 5. A process in accordance with claim 1, in which the nickel compound provides Ni nickel.
 6. A process in accordance with claim 1, in which the nickel compound is an inorganic nickel salt.
 7. A process in accordance with claim 1, in which the nickel compound is an organic nickel salt.
 8. A process in accordance with claim 1, in which the nickel compound is applied in the form of a solution in a liquid.
 9. A process in accordance with claim 1, in which the nickel compound is selected from the group consisting of nickel chloride, nickel sulfate, nickel nitrate, nickel carbonate and a nickel salt of an organic carboxylic acid.
 10. A process in accordance with claim 1, in which the nickel compound is applied in an amount to provide from about 5 to about 5,000 mg. of nickel per kg. of wood.
 11. Wood particles resistant to attack by the mold fungus Chrysosporium lignorum containing a growth-inhibiting amount of a nickel compound that supplies nickel in available or soluble form.
 12. Wood particles in accordance with claim 11 in which resistance to rot fungi is also provided.
 13. Wood particles in accordance with claim 11 in the form of wood chips.
 14. Wood particles in accordance with claim 11 in the form of cellulose pulp.
 15. Wood particles in accordance with claim 11, in which the nickel compound is present in an amount to provide from about 5 to about 5,000 mg. nickel per kg. of wood.
 16. Wood particles in accordance with claim 11 in which the nickel compound provides Ni nickel.
 17. Wood particles in accordance with claim 11 in which the nickel compound is an inorganic nickel salt.
 18. Wood particles in accordance with claim 11 in which the nickel compound is an organic nickel salt. 